Dang, so here's my dilemma, if I'm going to have to change the evaporator should I change to the R-134a parts for better efficiency? The cost is the same so maybe this is the time, Does anyone know if I can use my same compressor but change the condenser and evaporator? Even with all new parts sans compressor it'd only be about $300 to do the conversion.

I'll let you decide. Either way match up parts so you know they'll fit properly. Gets personal with 134a parts - they aren't as strong IMO especially the condensers up front one road stone they are gone. You can use buck shot at a tube and fin one and nothing goes wrong!

The "heat transfer" is what A/C is all about. The finer, thinner things are the more heat they can exchange however they can't tolerate any debris or be flushed effectively at all. It's just so easy to end up with something dumb and end up needing everything all over again and this a truck cab to cool unless you really want more BTUs than you already said was good I don't think it's worth it.

Had no choice with a condenser or didn't look hard enough and it worked fine so did the old one OE replaced because of an accident OE (not me) but rubbed a line thru radiator support that I couldn't weld or fix and it reduced known charge 10oz and said so on paper in the box.

At least there was no losing info on an exact charge to mess with all day to get right with unknowns. If you change it you may not get that info with it if needed at all,

Yeah I'm not sure if I want to do a full conversion, although then I could be sure it'd cool well with off the shelf refrigerants. I could use junk yard parts and probably get it accomplished for even less. The only thing i'm not sure about is the R-134a systems in these trucks had a high pressure cutoff switch, which I would guess my truck isn't wired for?

Forgot if already said now page 2 on this. At least a new LPCO switch should be adjustable - look for the screw inside with it unplugged. If old they still adjust you just risk it leaking from moving that screw. Just go part turns and keep count so you can go back to where you were or know where you are before touched if you do that. If new isn't adjustable go find a bunch of used ones they all fit and they don't all leak if touched. Still keep a coffee can full of them just for that,

Now you are going to ask me which way lowers cut out continuity and I'll guess wrong no doubt. I think you tighten (clockwise looking at it) will lower pressure that it cuts out. That's another reason if you touch it to only go no more than 1/2 turn, maybe 1/4 turn at a time.

I generally don't need to touch them but you have a concern on a refrigerant the truck wasn't meant for and IDK what the result would be.

If you allow a compressor to run too long when it SHOULD cut off not a maybe you will choke the compressor with liquid being returned at high risk of blowing all work up or lucky if only belt slips over stuck compressor.

All caution and AYOR with doing that if you do.

Don't forget new it still could leak right at the screw if touched. Best tested with a sniffer but think just a bubble test would show it and if so that one has to go right away not even back to where it was,